The present invention relates to a method for safely controlling burning of a fuel gas utilized for a gas turbine, for example.
Generally, when it is required to start the operation of a combustor of a gas turbine system for burning a fuel gas, a pre-purge operation of the residual fuel gas is first preliminarily carried out and then an actual burning is performed in the combustor. It is also recommended to arrange various safety devices to a control unit for the combustor.
In one typical example of a gas turbine system provided with such a fuel gas burning control unit, a combustor has an inlet portion which communicates with a main fuel passage connected to a fuel gas resource through which the fuel gas flows. Safety shut off valves, called safety valves hereinafter, a main shut-off valve and a flow regulating valve are incorporated in the main fuel passage in this order towards the combustor. A pressure detection switch and a control unit operatively connected to the pressure detection switch are also incorporated in the main fuel passage in order to detect the pressure of the fuel gas. A branch fuel passage is connected at one end to the main fuel passage at a portion just before the main shut-off valve and has the other end connected to the inlet portion of the combustor. A primary shut-off valve and a throttle means are incorporated in the branch fuel passage. The operations of these valves are controlled by an engine control box which is operatively connected to a starter motor.
In such a gas turbine system, after the start of operation the, a pressure of the fuel gas to be supplied to the combustor is measured by the pressure detection switch. In a case where the detected pressure value is outside of a controllable range, an alarm signal is transmitted from the control unit to the engine control box, and then the engine control box generates a signal to the safety shut-off valves and the main shut-off valve to close these valves and thereby stop the supply of the fuel gas to the combustor. A gas turbine system of the type described above is only equipped with such a control unit. Accordingly, at the time of operation start, i.e. ignition, of the combustor, if part of the fuel gas leaks through the main shut-off valve due to foreign particles for example attached to the valve sheets thereof, and enters into the combustor, there is the fear of causing abnormal burning, such as an explosion in an extreme case, resulting in breakage of the combustor itself, as well as ducts connected to the combustor.